尝试加载片段布局时，从onCreateView停止无限循环

Question

我正在尝试创建一个加载两个片段之一的活动。第一个片段（SendFragment）将有一个文本框和一个按钮，并将文本发送到第二个片段。然后第二个片段（DisplayFragment）将显示收到的文本。 MainActivity将首先加载SendFragment的布局，然后在发送文本时加载DisplayFragment的布局。

当应用程序启动时，调用onFreateView（）for SendFragment时会发生无限循环。循环在OnCreateView（）和行之间重复，以使SendFragment布局膨胀。

如何只加载一次布局并停止无限循环？

DisplayFragment.Java

package com.example.helloworld;

import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


/**
 * A simple {@link Fragment} subclass.
 * Activities that contain this fragment must implement the
 * {@link DisplayFragment.OnFragmentInteractionListener} interface
 * to handle interaction events.
 * Use the {@link DisplayFragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class DisplayFragment extends Fragment {
    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_MESSAGE = "param1";

    // TODO: Rename and change types of parameters
    private String message;

    private OnFragmentInteractionListener mListener;

    public DisplayFragment() {
        // Required empty public constructor
    }

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @return A new instance of fragment DisplayFragment.
     */
    // TODO: Rename and change types and number of parameters
    public static DisplayFragment newInstance(String param1) {
        DisplayFragment fragment = new DisplayFragment();
        Bundle args = new Bundle();
        args.putString(ARG_MESSAGE, param1);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            message = getArguments().getString(ARG_MESSAGE);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_display, container, false);
    }

    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    /**
     * This interface must be implemented by activities that contain this
     * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     * <p/>
     * See the Android Training lesson <a href=
     * "http://developer.android.com/training/basics/fragments/communicating.html"
     * >Communicating with Other Fragments</a> for more information.
     */
    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
    }
}

SendFragment.Java

package com.example.helloworld;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;


/**
 * A simple {@link Fragment} subclass.
 * Activities that contain this fragment must implement the
 * {@link SendFragment.OnMessageSentListener} interface
 * to handle interaction events.
 * Use the factory method to
 * create an instance of this fragment.
 */
public class SendFragment extends Fragment {

    private OnMessageSentListener mListener;

    View view;

    public SendFragment() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        if(view != null) {
            ViewGroup parent = (ViewGroup) view.getParent();
            if (parent != null)
                parent.removeView(view);
        }
        view = inflater.inflate(R.layout.fragment_send, container, false);
        return view;
    }

    // TODO: Rename method, update argument and hook method into UI event
    public void sendMessage(View v) {

        if (mListener != null) {
            EditText editText = (EditText) v.findViewById(R.id.edit_message);
            String message = editText.getText().toString();
            mListener.onMessageSent(message);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnMessageSentListener) {
            mListener = (OnMessageSentListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    /**
     * This interface must be implemented by activities that contain this
     * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     * <p>
     * See the Android Training lesson <a href=
     * "http://developer.android.com/training/basics/fragments/communicating.html"
     * >Communicating with Other Fragments</a> for more information.
     */
    public interface OnMessageSentListener {
        // TODO: Update argument type and name
        void onMessageSent(String s);
    }

}

MainActivity.Java

package com.example.helloworld;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;

public class MainActivity extends FragmentActivity
    implements com.example.helloworld.SendFragment.OnMessageSentListener {

    public final static String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Check that the activity is using the layout version with
        // the fragment_container FrameLayout
        if (findViewById(R.id.fragment_container) != null) {

            // However, if we're being restored from a previous state,
            // then we don't need to do anything and should return or else
            // we could end up with overlapping fragments.
            if (savedInstanceState != null) {
                return;
            }

            // Create a new Fragment to be placed in the activity layout
            SendFragment firstFragment = new SendFragment();

            // In case this activity was started with special instructions from an
            // Intent, pass the Intent's extras to the fragment as arguments
            firstFragment.setArguments(getIntent().getExtras());

            // Add the fragment to the 'fragment_container' FrameLayout
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.fragment_container, firstFragment).commit();
        }
    }

    public void onMessageSent(String s) {

        DisplayFragment display = (DisplayFragment)
                getSupportFragmentManager().findFragmentById(R.id.display_fragment);

        if (display != null) {

            // do something??

        }
        else {

            DisplayFragment newFragment = DisplayFragment.newInstance(s);

            FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

            // Replace whatever is in the fragment_container view with this fragment,
            // and add the transaction to the back stack so the user can navigate back
            transaction.replace(R.id.fragment_container, newFragment);
            transaction.addToBackStack(null);

            // Commit the transaction
            transaction.commit();

        }

    }
}

fragment_display.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.helloworld.DisplayFragment">

    <!-- TODO: Update blank fragment layout -->
    <fragment android:name="com.example.helloworld.DisplayFragment"
        android:id="@+id/display_fragment"
        android:layout_weight="1"
        android:layout_width="0dp"
        android:layout_height="match_parent">
    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="@string/hello_blank_fragment" />
    </fragment>

</FrameLayout>

fragment_send.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.helloworld.SendFragment">


    <fragment android:name="com.example.helloworld.SendFragment"
        android:id="@+id/send_fragment"
        android:layout_weight="1"
        android:layout_width="0dp"
        android:layout_height="match_parent">
    <LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal">

        <EditText android:id="@+id/edit_message"
            android:layout_weight="1"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:hint="@string/edit_message" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/button_send"
            android:onClick="sendMessage" />

    </LinearLayout>
    </fragment>


</FrameLayout>

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

Answer 1

将您的onCreateView()更改为 -

 @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        return  inflater.inflate(R.layout.fragment_send, container, false);
    }

更新 -

从您的两个片段中删除<fragment>组件＆＃39;布局。由于您已经动态初始化了片段，因此不需要这样做。

Answer 2

确保初始化期间任何LiveData<?> Observer都不会触发无限循环

LiveData<Boolean> eventHappened =
..
eventHappened.observe{
 do something
 eventHappened.value = false //infinite loop
}